The species of the genus Cimex (Heteroptera: Cimicidae) are important ectoparasites of European bats. Unlike other ectoparasites, they are attached to the body of their host only when they need to feed, otherwise they stay in refugia in bat roosts. Consequently, they are often overlooked by bat specialists and in many countries they are either unknown or poorly characterized. This study reports results from thorough investigations of bat roosts of diverse bat species in a Northwest-Southeast transect across Europe: Czech and Slovak Republics, Hungary, Serbia and Bulgaria. The distribution of Cimex lectularius follows the synanthropic habitats
of its principal hosts, Myotis myotis and M. emarginatus, both Mediterranean elements of the European fauna. The climate in natural roosts (i.e. caves) inhabited by these bats in southern areas appears to restrain the presence of cimicids. In central Europe, C. pipistrelli parasitizes, beside M. myotis, many crevice-dwelling bat species indigenous to the boreal zone. However, in southern Europe, it appears only in connection with Nyctalus noctula. C. lectularius was confirmed for five host bat species and newly recorded for
Rhinolophus ferrumequinum, C. pipistrelli was confirmed for seven bat species and newly recorded for Myotis nattereri. The first record of C.
emarginatus outside of its type locality and Myotis alcathoe as a new host are reported. The host preferences of the species of the genus Cimex
are discussed.